A 3 MV NEC 9SDH-2 Pelletron accelerator is installed at the Center for Isotopic Research on Cultural and Environmental Heritage of Dipartimento di Matematica e Fisica, Università degli Studi della Campania “Luigi Vanvitelli”, Caserta (CIRCE-DMF). The accelerator serves several beam lines devoted to both applied and fundamental research. While generally a precise and accurate knowledge of the energy of the charged particle beams is of interest for all applications, the measurement of charged particle nuclear reactions of astrophysical energies is particularly demanding because of the strong energy dependence of the cross section below the Coulomb barrier and the very long duration of the measurements. We describe here the energy calibration of the accelerator installed at CIRCE-DMF and a measurement of the short term stability. A routine to improve the long term stability and remove the observed dependence of the terminal voltage on the injected current was successfully tested. Finally, possible improvements are discussed
